There are two problem types in this module: medication given in divided doses and reconstitution of powdered medications.
Problems will involve reading medication labels and healthcare provider’s orders. You will calculate the correct amount to give a client of oral, injectable, and intravenous medications. Assume all questions ask for the amount per dose unless instructed otherwise.
You should now know all your commonly used equivalents.
You will continue to use the rounding rules for numbers >1 and <1.
You will also need to refer to your rounding rules for tablets and capsules.
The SF in most of the problems is the amount of medication the healthcare provider has prescribed. The dose is usually stated in mg, mcg, or g.
Weight-based medications will use the client’s weight as the SF.
The healthcare provider may prescribe the total amount of a medication to be given in a day (24 hours). The medication prescription may state that the medication is to be given in a specific number of doses (for example, four times daily). The medication prescription may state that the medication is to be given after a certain amount of time has passed (for example, every 6 hours). Note that the two intervals stated as examples are really the same. Every 6 hours is the same as 4 times daily.
The nurse will calculate the amount to give for the entire day then divide the ordered number of dose. Note: do not round the quantity of medication until the amount per dose is calculated. Rounding before the amount per dose is calculated may result in an incorrect quantity per dose and in total.
If the problem does not state divided doses, the prescription is written for one dose.
https://www.drugs.com/pro/images/5fc0e987-61c9-40c4-b0d5-fcea07c8733e/ativan-injection-7.jpg Retrieved 2/5/19
Example 1:
A healthcare provider has prescribed lorazepam 4 mg IM in six divided doses. How much will the nurse give per dose?
Here’s the problem set up in the dimensional analysis format:
SF = 4 mg
AU = ml per dose
Equivalents:
4 mg = 1 ml (see the drug label)
Equation for the dose in ml:
https://www.drugs.com/pro/images/c7d61d98-fe86-4340-9b86-47eb92acaa0e/zofran-oral-spl-graphic-07.jpg Retrieved 2/5/19
Example 2:
A healthcare provider has prescribed ondansetron HCl 24 mg orally daily in divided doses every 8 hours. How many ml will the nurse give per dose?
SF = 24 mg
AU = ml per dose
Equivalents:
4 mg = 5 ml (see label)
Equation for the dose in ml:
Some medication is supplied in a powdered form and must mixed with a specified liquid (diluent) before it is used.
http://www.austincc.edu/rxsucces/pdf/reconstructionpdf.pdf Retrieved 1/27/19
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Instructions for reconstitution will be provided on the drug label or package insert. Be certain that you are using the correct diluent in the correct quantity for each medication,
In the label above, 2.7 ml of sterile water is the specified diluent for oxacillin sodium. First inject 2.7 ml of air into the vial of sterile water to compensate for the volume of fluid to be removed. Then withdraw 2.7 ml of sterile water to use as the diluent.
Inject the sterile water into the vial of powdered medication. Swirl or rotate to mix as directed. The medication is then ready to use. The date and time of reconstitution and the nurse’s name must be recorded on the vial of medication because medication must not be used after its shelf life has expired.
The dosage strength of the reconstituted medication will be specified on the label. The dosage strength of the reconstituted medication is the strength the nurse will use in calculating the amount of medication to give the client according to the healthcare provider’s prescription.
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Some medications will give a range of diluent amounts, each resulting in a different dosage strength of the medication. See the right side of the medication label above. The amount of diluent to use will be selected based on the dose to be given. The amount of diluent used must be recorded so the dosage strength will be clear to anyone using the reconstituted medication.
Recording the amount of diluent used will prevent possible medication errors due to a misunderstanding of the medication dosage strength.
https://www.drugs.com/pro/images/bf92a7d7-395b-4e2c-a3c4-66ebdbfd1052/fpl-bl-40mgperml-35ml-06.jpg Retrieved 1/27/19
Example 1:
The healthcare provider has prescribed fluconazole oral suspension 200 mg by mouth daily for 7 days. How many ml will the nurse give to the client per dose?
SF = 200 mg
AU = ml
Equivalents:
Note - The nurse has added 24 ml of distilled or purified water to the powdered medication for reconstitution, but this amount is not relevant in calculating the dose to give. The label states the drug strength after reconstitution.
40 mg = 1 ml
Equation for the dose in ml:
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Example 2:
The healthcare provider has prescribed 2 g streptomycin IM daily divided every 8 hours for your client. Your charge nurse recommends that you use 1.8 ml of sterile water to reconstitute the medication to reduce the volume to be injected. How many ml will you give per dose?
SF = 2 g
AU = ml per dose
Equivalents:
1 g = 1000 mg
400 mg = 1 ml (from the reconstitution directions on the label)
You do not use the 1.8 ml of diluent added in your calculations, but you need this information to find the 400 mg per ml after reconstitution from the drug label.
Equation for the dose in ml:
Please notice:
One day = 24 hours
Every 8 hours = 3 doses per day
Module 6 Practice Problems
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Use the Adderall XR label above for problems 1 and 2.
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Use the Benadryl label above for problems 3 and 4.
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Use the label for Dilantin-125 above for problems 5 and 6.
http://drugsdb.eu/images/ondansetron_hydrochloride_Ondansetron-injection-2ml-label.jpg Retrieved 2/5/2019
Use the label for ondansetron injection above for problem 7.
https://medlibrary.org/lib/images-rx/tobramycin-sulfate-2/80cdc563-140a-404f-bbcd-eaef1684b705-04.jpg Retrieved 2/5/2019
Use the tobramycin label above for problem 8.
https://medlibrary.org/lib/images-rx/phenergan/7f845a30-d055-452d-957f-a8be87f52815-03.jpg Retrieved 2/5/2019
Use the Phenergan injection label above for problems 9 and 10.
https://www.rxresource.org/image.php?src=75ca51d0-343c-48c2-9873-2a3c45e8ffe8/250mg-80ml-label.jpg Retrieved 2/5/2019
Use the label above for amoxicillin oral suspension for problems 11 and 12.
https://aidsinfo.nih.gov/images/xml-images/0069-3150-83/zithromax-iv-03.jpg Retrieved 2/5/2019
Use the Zithromax label above for problems 13 and 14.
https://www.drugs.com/pro/images/8f7b3ac0-604d-4c78-b545-5e0f8ea3d698/dan00-0001-03.jpg Retrieved 1/27/19
Use the label for Ryanodex for questions 15 and 16.
https://clinicalgate.com/wp-content/uploads/2015/03/B9781437723663000114_b011-013-9781437723663.jpg Retrieved 1/27/19
Use the Pfizerpen label above for questions 17 through 20.
A nurse is working on a hospital medical unit and has several clients with prescriptions for penicillin G potassium IV.
Why do you often need the client’s age? Doses of the medication often differ by age, especially when the clients are children or teens.
The Adderall XR questions:
SF = 60 mg
AU = capsules
Equivalents:
1 capsule = 15 mg
2 doses
Equation for the dose in caps:
SF = 45 mg
AU = capsules
Equivalents:
1 capsule = 15 mg
3 doses
Equation for the dose in caps:
The Benadryl questions:
SF = 40 mg
AU = mL
Equivalents:
5 mL = 12.5 mg
4 doses
Equation for the dose in mL:
SF = 60 mg
AU = mL
Equivalents:
5 mL = 12.5 mg
4 doses
Equation for the dose in mL
The Dilantin questions:
Remember: In weight-based problems, the client’s weight is the starting factor. If the weight is in pounds and the prescription is in kg, a weight conversion should be built into your equation.
SF = 125 lbs
AU = mL
Equivalents:
5 mL = 125 mg
1 kg = 2.2 lbs
3 doses
Equation for the dose in mL:
In this problem there is no difference in the answer, but remember to not round your answer to the appropriate number of decimal places until you reach your final answer.
SF = 55 kg
AU = mL
Equivalents:
5 mL = 125 mg
3 doses
Equation for the dose in mL:
The Ondansetron question:
SF = 24 mg
AU = mL
Equivalents:
1 mL = 2 mg
3 doses
Equation for the dose in mL:
The Tobramycin question:
SF = 180 lbs
AU = mL
Equivalents:
1 mL = 40 mg
1 kg = 2.2 lbs
3 doses
Equation for the dose in mL:
The Phenergan questions:
SF = 100 mg
AU = ml
Equivalents:
1 mL = 25 mg
3 doses
Equation for the dose in mL:
SF = 80 mg
AU = mL
Equivalents:
1 mL = 25 mg
3 doses
Equation for the dose in mL:
The Amoxicillin questions:
The diluent is water. You are to add 59 mL of water to the powder.
SF = 1300 mg
AU = mL
Equivalents:
5 mL = 250 mg
3 doses
Equation for dose in mL:
SF = 400 mg
AU = mL
Equivalents:
5 mL = 250 mg
Equation for dose in mL:
This problem is not written for divided doses. The dose stated will be given every 8 hours.
The Zithromax questions:
SF = 500 mg
AU = mL
Equivalents:
1 mL = 100 mg
Equation:
This problem is not written for divided doses. The dose stated will be given every day.
The medication label states to dilute further before use. That would be done after the correct dose is drawn from the vial.
SF = 450 mg
AU = mL
Equivalents:
1 mL = 100 mg
Equation:
This problem is not written for divided doses. The dose stated will be given every day.
The medication label states to dilute further before use. That would be done after the correct dose is drawn from the vial.
The Ryanodex questions:
SF = 150 lbs
AU = mL per dose
Equivalents:
1 mL = 50 mg
1 kg = 2.2 lbs
Equation:
This problem is not written for divided doses.
The diluent is sterile water for injection (supplied in a vial).
SF = 150 lbs
AU = mL per dose
Equivalents:
1 mL = 50 mg
1 kg = 2.2 lbs
Equation:
This problem is not written for divided doses.
The Pfizerpen questions:
SF = 10,000,000 units
AU = mL
Equivalents:
1 mL = 250,000 units
4 doses
Equation:
SF = 20,000,000 units
AU = mL
Equivalents:
1 mL = 500,000 units (see label – amount of diluent has changed)
6 doses
Equation:
SF = 30,000,000 units
AU = mL
Equivalents:
1 mL = 250,000 units (see label – diluent has changed again)
6 doses
Equation for the dose in ml:
SF = 25,000,000 units
AU = mL
Equivalents:
1 mL = 250,000 units
4 doses
Equation: